SAT II Physics : Doppler Effect
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Example Questions
Example Question #1 : Doppler Effect
A train blows its whistle as it approaches a station at 
Wave frequency is distorted when the observer or source is in motion based on the Doppler effect. The equation for the Doppler effect is:
Terms in the numerator are summed if the observer moves toward the source. Terms in the denominator are summed if the source is moving away from the observer.
In this question, the train (source) is moving toward the observer. This means that the denominator terms will be subtracted. The velocity of the observer is zero, giving us our final equation:
Use the given values for the emitted frequency, velocity of the train, and speed of sound to solve this equation.
Example Question #2 : Doppler Effect
A dog is stationary in someone's front yard and barks at a frequency of 
The observer is moving away from the dog
The observer is traveling in circular path with the dog at the center of the circle
Both the dog and the observer have the same acceleration
The observer is moving towards the dog
Both the dog and the observer have the same velocity
The observer is moving towards the dog
The doppler effect states that the observed frequency depends on the frequency produced, and the relative velocities of the observer and sound source:
To increase the observed frequency the sound source and the observer must be moving towards each other. Since the dog is stationary, therefore the observer must be moving towards the dog.
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